Dehydrocyclization of aliphatic hydrocarbons



.Patented'Oct. 1945 Vladimir N. Ipatiefl and Vladimir Haensel, Chicago,111., assignors to' Universal Oil Products Company, Chicago, Ill., acorporation of Delaware No Drawing.

6 Claims. (01160 -6735) This invention relatesto the, dehydrogenation toproduce aromatics therefrom and is characterized by the'use ofparticular types of catalysts which have been found to be especiallyeflective I for this purpose,

and dehydrocyclization ofaliphatic hydrocarbons.

The invention is more specifically concerned with the use ofcoordinatedconditions of temperature, pressure and space velocity when employingthe particular types of catalysts which will be presently described.

The principal value of processes for the dehy-' drocyclization ofaliphatic hydrocarbons lies in the fact that by this reaction,particularly when catalysts are used, high yields oi aromatic hydro--carbons are produced having the same number of carbon atoms as thealiphatic hydrocarbons treated whereas when aromatic hydrocarbons aremade by the intensive and non-catalytic crackin of petroleum and coaltars, there is a large production of undesirable by-products includin onthe on hand hydrogen and low-boiling hydrocarbons which are gaseousunder normal con- Application December 24, 1941, Serial No. 424,276 Iular alumina suspended in aqueous solutions, containing salts of bothzinc and copper, by the addition of ammonium carbonate or alkali metalcarbonates to the solutions. Precipitations are usually carried out at atemperature of approximately 80? 0., although the precipitating reagentmay be added at ordinary temperatures and thesolution'then heated toabout 80 C. after which the suspended material is filtered; washedsubstantiallrd'ree of absorbed .or occluded salts. heated' atapproximately 250 D formed into particles oLreguIated size such as, forexample, small cylindrical pellets by custoniary'procedures and thenreduced by hydrogen or hydrogen-contaming gas mixtures.

In catalysts thus prepared reducing conditions are preferably employedwhich almost completely reduce the copper oxide to metallic copper butditions and on the other hand heavier tars and coke. There are. furtherdimculties encountered in the separation of thearomatics produced onaccount of the formation of polycyclic ring com pounds such asnaphthalene, anthracene, phenanthrene, etc. When a given hydrocarbon,such as for example, hexane is dehydrogenated in the presence ofproperly selected catalysts and under suitably related conditions ofoperation, yields of benzol which do not reduce the zinc oxide to anyextent.

By this means greater stabilhty of the catalyst is assured since therewill he s bstantially no volatilization of zinc at the conditionsemployed when hydrocarbons are treated. It is good practice tohave thefinally prepared catalyst consist of about 15 per cent zinc oxide, 5 percentcopper and 80 per cent alumina by weight, although altematlvecatalysts of good activitymay comprise found that pelleted materialscontaining over thisnot less than about 5% zinc oxide, not more thanabout 10% copper and the remainder alumina.

While the higher percentages of copper may give initially highercatalytic activity, it has been percentage have lower crushing strengthsso that much higher than those obtainable by non-catalytic cracking maybe obtained. Similarly, high yields of aromatics may beobtained bydehydrocycling analogous unsaturated hydrocarbons containing at least 6carbon atoms in straight chain arrangement, including alkenes, alkynesand alkadienes, although conditions of operation when e stockswil bedifierent than those employed. in the case of corresponding paraiiinhydrocarbons. In one specific embodiment the present invention comprisesthe treatment of aliphatic hydro-- carbons for the production ofsubstantial yields sists in subjecting said aliphatic hydrocarbons atelevated temperatures to contact with composite catalysts comprisingessentially zinc oxide, cop.-

per and alumina. v I v Jl'hesctq-llsts wmch characterize the presentinvention are'preierablyprepared by a series of steps involving firstthe precipitation of the carbonates of zinc and copper, upon preparedgranm. loying these unsaturated charging of aromatic hydrocarbonstherefrom which con- UF alu'mina develops which is not as good a cartheyare inclined to develop fines on handling. If the catalysts are to beused in the 'form of a powder, the relative amounts of the zinc oxide,copper and alumina can be varied over a wider range in case advantagesare gained thereby. In-

stead of concurrently precipitating zinc and copper carbonates, they maybe deposited successively upon the alumina.

The alumina employed as a relatively inert supporting or carryingmaterial for the zinc oxide and copper is preferably of the so-called"activated variety which is prepared by the con-; trolled heating ofeither precipitated hydrous oxides-of alumina, or natural minerals suchas.

sibb'site, hydrargiliite or bauxite at temperatures of the order of 500C. which corresponds" to only partial dehydration and the presence ofrelatively large amounts of gamma alumina. If the original hydrous orhydrated oxides are heated at much higher temperatures of from about 800to about 900 C., the alpha form of rier' for the active components ofthe catalyst composites. Completely dehydrated alumina is not suitablein the present types of catalyst com- In utilising the described typesof catalysts for producing aromatics from aliphatic hydrocarboss, thetemperatures employed will vary'from about 450 to about 850 6.,depending upon the type of aliphatic treated, its molecular weight.

boiling point, etc. Best results are usually obtained -at approximatelyatmospheric pressure and at liquid space velocities varying from about0.1 to about volumes of liquid charge per hour per volume of catalystpace. when cycling olefins, dioleflns or acetylenes, best conditions ofoperation will usually include the use of subat- 'mospheric pressureswith space velocitieswithin the lower ranges of thou: specified, theseconditions tending to lessen the formation of carbon from undesirableside reactions due to the decomposition of the unsaturatedcompoimds.

In the 0 operation of the process a hydrocarbon or mixture ofhydrocarbons to be treated is vaporized, heated to an optimumtemperature in the rangespecined and passed throughabedofgranularcatalystsataspace veiocityfound by trial to produce the bestresults. Reactions of cyclization are endothermic and it is convenientto employ reactors of the adiabatic type, the vapors of the hydrocarboncharge being admitted to the catalyst chamber at a temperature somewhatabove the optimum and leaving at a temperature somewhat below.

After being discharged from the reactor the products are subjected tofractionation to separate hydrogen and other fixed gases, the aromatichydrocarbons formed and unconverted materials which it may be desired torecycle for further treatment. After a period of hydrocarbon processing.the catalysts gradually accumulate some carbonaceous deposits whichmaybe periodically burned off by the use of oxidizing gas mixtures whileother reactors in parallel connection are operating upon the charge tothe plant. a

In some instances improved results particularly-in respect to carbondeposits may be obtained when limited amounts of hydrogen are added tothe vapors of the hydrocarbon under:- going dehydrocyclization, thiseffect being probably due to the suppression of cracking reactions. Thefollowing data showing the results of experiments' are introduced toillustrate the char- I acter of the results obtainable when aliphatichydrocarbons are converted to aromatic hydrocarbons while in contactwith the present types of catalysts, although neither examples ofcatalyst manufacture nor of their use in dehydro- .eycilzation areindicated to unduly limit the scope of the invention.

The method of preparing catalysts of the pres-" enlt1 ctharacter isexemplified in the following dese p i0n:.

183 parts by weight of zinc nitrate and 23.7

parts by weight of copper nitrate were dissolved in 1000 parts by weightof water and added to a rapidly agitated suspension of 192.5 parts byweight; of aluminum oxide. in 2500 parts of water. The'entire materialwas heated to 80-85 C. and

. 81 parts by wei'ghtnf ammonium carbonate were dissolved in 500 partsby water and added to the hot suspension. After the addition of theammonium carbonate solution, the spension. now c n isti s of basic cpper'carbonate, ainc carbonate and aluminum oxide, was cooled withoutagitating and finally washed by dccantation.

This was followed by filtering and further washing. The precipitate wasdried at 250 C. for 10 hours and reduced with hydrogen at 225? .C. for 1hour using a mixture of about one volume of hydrogen and about threevolumes of nitrogen.

' The reduced catalyst, now consisting essentially of copper, zinc oxideand alumina, was pelleted using a hydrogenated cocoanut oil as alubricant. The pilled catalyst was treated with air to remove thelubricant and again reduced 'witha-hydrogen-nitmgen mixture at theoperating temperature.

The composition of the reduced catalyst as determined by analysis wasapproximately as follows: 5

21:0 Y v 15.0 c 5.4 Ah0.| 79.6

Two catalysts prepared as above described and designated below as Aand Bwere used-for the production of toluene from normal heptaneundersubstantially atmospheric pressure and at tem- It can be seen frontthe above data that at a relatively constant temperature best resultsare obtained on both catalysts A and B when using space velocities ofthe order of 0.23 and 0.31 respectively. It is to be noted also that theactivity .of both catalysts was not reduced, but rather restored andeven improved after regeneration. By recycling of the unconvertedheptane the ultimate yield of toluene was raised to about per cent inrun 2.

' The data given in thefollowing table include those obtained on furtherruns with catalyst B at varying temperatures and show-that bestonce-through yields are obtained at the furnace temperature of 537 C.

Duration Temp. Av. hourly Wt. per

Run No. of run, 0. liquid s ace cent yield hours furnace vsl ty oftoluene The following data indicate the efiect on carhon deposits whenusing hydrogen in connection with the present types of catalysts.CatalystB was used to dehydrocycle normal heptane andthe following tableshows the conditions of opera- Av. hourly Vol Wt. per ydro- Wt. per RunNo. $231 13 g g gen/voLhepcent yield fi s;

Vela-city tans of toluene catalyst 1 s31 6.94 0 31.2 as: 2-; 536 0.94500 32.0 1.46

We claim asour invention: I

1. A process for the treatment of an aliphatic comprising essentiallyzinc oxide,

hydrocarbon containing at least 6 carbon atoms in straight-chainarrangementto produce substantial yields of aromatic hydrocarbonstherefrom which comprises subjecting said aliphatic hydrocarbon tocontact with a composite catalyst copper and alumina.

2. A process for the treatment of a parafiin hydrocarbon containing atleast six carbon atoms in straight-chain arrangement to producesubstantial yields of aromatic hydrocarbons there- 'from which comprisessubjecting said parafiin hydrocarbon to contact with a compositecatalyst comprising essentially zinc oxide, copper. and alumina.

3. A process for the treatment of a paraflin hydrocarbon containing atleast six carbon atoms in straight-chain arrangement to producesubstantial yields of aromatic hydrocarbons therefrom which comprisessubjecting said paramn with a composite catalyst comprising essentiallyzinc oxide, copper and alumina, the weight per cent of zinc oxide insaid composite being not less than 5, and the weight per cent of copperbeing not greater than 10.

5. A process of the treatment of an olefin hydrocarbon containing atleast six carbon atoms in straight-chain arrangement to producesubstantial yields of aromatic hydrocarbons therefrom which comprisessubjecting said olefin hydrocarbon at a temperature of from about 450 toabout 650 C. under subatmospheric pressure and at a liquid hourly spacevelocity of from about 0.1 to about 5.0 to contact with a comhydrocarbonat a temperature of from about 450 ,to about 650 C. and at a liquidhourly space than 10;

posite catalyst comprising essentially zinc oxide, copper and alumina.

6. A process for the treatment of an olefin-hy drocarbon containing atleast six carbon atoms in straight-chain arrangement to producesubstantial yields of aromatic hydrocarbons therefrom which comprisessubjecting said olefin hydrocarbon at a temperature or from about 450 toabout 650 C. under subatmospheric pressure and at a liquid hourly spacevelocity of from about 0.1 to' about 5.0 to contact with a composite 4catalyst comprising essentially zinc oxide, copper and alumina, theweight per cent of zinc oxide in said composite being not less than 5and the weight per cent of copper being not greater VLADIMIR N.IPATIEFF. vrnnnwm rmnusnn

